https://opencores.org/websvn/filedetails?repname=spi_master_slave&path=%2Fspi_master_slave%2Ftrunk%2Frtl%2Fspi_master_slave%2Fspi_master.vhd
* Wishbone-compliant <https://opencores.org/project,simple_spi>
* Raptor Engineering litespi, improved <https://gitlab.raptorengineering.com/kestrel-collaboration/kestrel-litex/litespi>
https://opencores.org/websvn/filedetails?repname=spi_master_slave&path=%2Fspi_master_slave%2Ftrunk%2Frtl%2Fspi_master_slave%2Fspi_master.vhd
* Wishbone-compliant <https://opencores.org/project,simple_spi>
* Raptor Engineering litespi, improved <https://gitlab.raptorengineering.com/kestrel-collaboration/kestrel-litex/litespi>